1. Field of the Invention
The present invention relates to a method of manufacturing an ink jet recording head and a method of manufacturing a recording head using the substrate manufactured by this method.
2. Related Background Art
An ink jet recording head that has, as its component parts, an orifice provided to discharge a liquid and a heat acting portion (a heat generating portion), which is a portion in communication with this orifice and in which heat energy to discharge liquid droplets acts on the liquid, is described, for example, in FIGS. 1 and 3 of the Japanese Patent Application Laid-Open No. S60-159062. A structure corresponding to FIG. 1 of this patent publication is shown in FIG. 9. In this structure, a heat generating resistive layer 204, which generates heat when it is energized, is provided on a lower layer 202 of a substrate 200, and a pair of electrodes 203 is provided on the heat generating resistive layer 204 for one heat generating portion. Furthermore, on the heat generating resistive layer 204 and the electrode layers 203 there are provided an insulative protective layer 205 to protect these layers 204 and 203 from ink, and on the insulative protective layer 205 there is provided a metal protective layer 206 to protect the insulative protective layer 205 from cavitation that occurs when bubbles formed by the bubbling of the ink disappear. A structure corresponding to FIG. 3 of the Japanese Patent Application Laid-Open No. S60-159062 is shown in FIG. 10. This structure is the same as the structure shown in FIG. 9, with the exception that the vertical arrangement of the electrode layers 203 and the heat generating resistive layer 204 is reversed from that of FIG. 9.
For example, in FIG. 9, end portions 203a of the two electrode layers 203 fronting on a heat generating portion 207 are formed in such a manner as to have some inclination. However, the closer to perpendicularity to the heat generating resistive layer 204 the inclination of the end surfaces 203a, the more imperfect covering portions will be formed in the insulative protective layer 205 that covers a rising portion 210 from the heat generating resistive layer 204 of the end surface 203a, with the result that the insulative protective layer 205 may sometimes be unable to exhibit its function of insulation. Therefore, when the electrode layer 203 is provided so that the inclination of the end surface 203a forms a small angle with the heat generating resistive layer 204, the bottom end portion of the end surface 203a with a more acute angle (the leading end portion of the inclination of the end surface 203a) is broken or the area of the heat generating resistive layer (heat generating portion) positioned between the pair of electrode layers 203 varies due to errors in the position accuracy of the bottom end of the end surface 203a that occur during the formation of the electrode layer 203 and the like. As a result of this, variations occur in the calorific value of the heat generating portions 207. This poses a problem to be solved when a record image of higher grade is sought.
In FIG. 10, a pair of electrode layers 203 are provided on a lower layer 202 in such a manner as to sandwich a heat generating portion 207, and a heat generating resistive layer 204 is provided on the electrode layers 203. In the case of this construction, the heat generating resistive layer 204, the material itself used for which is hard, covers the electrode layers 203 as a relatively hard layer and, therefore, thermal deformation of the electrode layers 203 (for example, a hillock that occurs when the electrode layers are formed from aluminum) does not occur even when an insulative protective layer 205 to be formed on the heat generating resistive layer 204 is formed at a high temperature. Therefore, it is possible to form an insulative protective layer 205 in a dense manner and the layer thickness can be made small. As a result of this, the heat from the heat generating portion 207 can be transmitted to ink more efficiently.
However, even in the structure of FIG. 10, in addition to problems posed by the angle of the leading end of an end surface 203a of the electrode layer 203 and variations in the area of the heat generating portion as in the case of the structure of FIG. 9, the closer to perpendicularity to the lower layer 202 the end surface 203a, the worse the film quality of the heat generating resistive layer 204 that covers a rising portion 210 of the end surface 203a than other parts when the heat generating resistive layer 204 is formed on the electrode layer 203, thereby posing a further problem. Therefore, when a heat generating resistive body constituted by the pair of electrode layers 203 and the heat generating resistive layer 204 is driven, current concentration occurs in the heat generating resistive layer 204 at the end surface 203a opposed to the pair of electrodes 203 (the portion where a level difference with respect to the lower layer 202 is formed), the temperature rises locally and thermal stresses may be generated. This poses a problem. In addition to these problems, when a heat generating resistive body is continuously driven at high frequencies in order to adapt to high speed, high definition recording for which requirements are increasing today, there is a strong possibility that stronger thermal stresses may be generated, thereby causing broken wires in the heat generating resistive layer.